1. Field of the Invention
The present invention relates to a process for producing a stable aqueous sol of colloidal silica having a flat particulate shape. This silica sol forms a film when dried on a substrate and hence finds use in the coating and other application areas.
2. Description of the Prior Art
U.S. Pat. No. 2801902 mentions that a sol of negatively charged spherical colloidal silica (5-100 nm in diameter) turns into a sol of platy colloidal silica, with individual particles consisting of spherical colloidal silica particles joined to one another two-dimensionally, when heated after the addition of a cationic surface active agent.
Japanese Patent Laid-open No. 278114/1987 discloses a process for producing minute platy silica particles by heating, after the addition of an anionic surface active agent to a sol of positively charged colloidal silica coated with alumina, titania, zirconia, thoria, or the like.
These known processes consist of adding a surface active agent to the sol for the planar aggregation of colloidal silica particles and heating the sol for the joining of aggregated colloidal silica particles to one another.